Thermal insulation and flame-retardant type aluminum plate surface functional coating and preparation method thereof

Abstract

The present application relates to the technical field of coating composition, and particularly relates to a heat-retaining and flame-retarding type aluminum plate surface functional coating and a preparation method thereof, which comprises the following steps: copolymerizing diethyl ethylene phosphonate, glycidyl methacrylate and isobornyl methacrylate to obtain a ternary random copolymer, modifying hydrophobic silica aerogel by amination, preparing a core-shell type aerogel functional filler by epoxy-amino covalent grafting, then mixing the core-shell type aerogel functional filler with an intumescent flame-retardant system, titanium dioxide, a water-based silicone-acrylate emulsion and additives to obtain a coating, and finally coating the coating on the surface of a pretreated aluminum alloy plate and curing the coating into a film. The process solves the problem of poor compatibility between traditional coating inorganic fillers and organic matrix, and the problem of mutual restriction between heat-retaining and flame-retarding performance, and the prepared coating is excellent in heat-retaining, flame-retarding, smoke-suppressing and mechanical performance.

Description

Technical Field

[0001] This invention relates to the field of coating composition technology, and in particular to a heat-insulating and flame-retardant functional coating for aluminum plate surface and its preparation method. Background Technology

[0002] Thermal insulation coatings on aluminum plates achieve their insulation effects primarily through three mechanisms: heat reflection, heat barrier, and heat radiation. Heat-reflective coatings typically incorporate high-refractive-index functional fillers to reflect most solar radiation, reducing heat absorption. Heat-barrier coatings utilize hollow fillers to create numerous static air layers, extending the heat conduction path and reducing heat transfer efficiency. Heat-radiative coatings, on the other hand, use materials with high emissivity in the atmospheric window band to dissipate absorbed heat as infrared radiation. The flame-retardant mechanisms of flame-retardant coatings on aluminum plates mainly include cooling insulation, gas-phase flame retardancy, and condensed-phase flame retardancy. Cooling insulation relies on the endothermic decomposition reaction of the flame retardant to consume a large amount of heat, thereby reducing the temperature of the coating and substrate. Gas-phase flame retardancy releases inert gases such as nitrogen and carbon dioxide through decomposition, diluting the concentration of oxygen and combustible gases while capturing free radicals in the combustion chain reaction. Condensed-phase flame retardancy catalyzes the dehydration and cross-linking of film-forming substances to form a dense carbon layer, effectively isolating oxygen and heat transfer. Traditional flame-retardant coatings mostly use halogen-based flame retardants. Although they have high flame-retardant efficiency, they produce a large amount of toxic and harmful gases and fumes during combustion, posing a threat to the environment and human health. Therefore, they have been gradually replaced by environmentally friendly flame retardants. Currently, phosphorus-based, nitrogen-based, inorganic hydroxide, and intumescent flame-retardant systems have become the mainstream in research and application. Among them, the intumescent flame-retardant system consists of three parts: an acid source, a char source, and a gas source. When heated, it can rapidly expand to form a thick, porous char layer, which has excellent heat insulation and oxygen barrier effects.

[0003] The invention patent with patent publication number CN105330335A discloses a method for preparing a coating structure with flame-retardant and heat-insulating functions, including: spraying a flame-retardant and heat-insulating slurry onto the surface of a substrate by spraying to form a substrate with a coating; wherein the flame-retardant and heat-insulating slurry is composed of the following raw materials in weight percentages: 20-40% nano-silica aerogel, 10-30% nano-alumina sol, 30-50% deionized water, 4-17% asbestos fiber and 0.3-3% dispersant.

[0004] However, inorganic insulating fillers and organic or inorganic binder matrices are generally bonded only through physical interactions, lacking effective chemical bonding. This leads to filler agglomeration and weak interfacial adhesion, resulting in numerous defects within the coating. Under temperature changes and mechanical vibration, these defects are prone to cracking and peeling. Furthermore, interfacial defects create channels for moisture and corrosive media to penetrate, accelerating the corrosion of the aluminum substrate. To achieve basic flame-retardant effects, existing technologies often require the addition of large amounts of inorganic flame-retardant fillers or the use of harmful reinforcing materials such as asbestos fibers. This not only significantly increases the thermal conductivity of the coating, weakening its insulation performance, but also severely degrades its adhesion, flexibility, and other mechanical properties. Moreover, most products rely solely on a single thermal barrier mechanism for insulation, lacking the synergistic effect of heat reflection and radiation mechanisms, resulting in limited insulation efficiency. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a heat-insulating and flame-retardant functional coating for aluminum plates and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a heat-insulating and flame-retardant functional coating on the surface of an aluminum plate includes the following steps:

[0008] S1. Diethyl vinylphosphonate, glycidyl methacrylate and isobornyl methacrylate are dissolved in an organic solvent and copolymerized under the action of an initiator. The product is precipitated, washed and dried to obtain a ternary random copolymer.

[0009] S2. Disperse hydrophobic silica aerogel powder in a mixed solvent, add silane coupling agent, carry out hydrolysis and condensation reaction, and obtain aminated aerogel by centrifugation, washing and drying.

[0010] S3. The aminated aerogel is redispersed in an anhydrous organic solvent, a ternary random copolymer is added, the mixture is stirred and reacted, and after the reaction is completed, it is washed, centrifuged and dried to obtain the aerogel functional filler.

[0011] S4. Mix aerogel functional filler with an intumescent flame retardant system, titanium dioxide, water-based silicone-acrylic emulsion and additives, add deionized water, and then disperse, mill and adjust the paint to obtain a heat-insulating and flame-retardant functional coating.

[0012] S5. Apply the heat-insulating and flame-retardant functional coating to the surface of the pretreated aluminum alloy plate, and then dry and cure it to form a functional coating.

[0013] Further, in step S1, the mass ratio of diethyl vinylphosphonate, glycidyl methacrylate, and isobornyl methacrylate is (2.08-4.17):1:(3.13-6.26); the initiator is selected from azobisisobutyronitrile, and its addition amount is 0.8-1.2% of the total mass of diethyl vinylphosphonate, glycidyl methacrylate, and isobornyl methacrylate; anhydrous methanol or anhydrous ethanol is used as the precipitant, and the volume ratio of the precipitant to the reaction solution is (3-5):1.

[0014] Further, the copolymerization reaction in step S1 is carried out under inert gas protection, the temperature of the copolymerization reaction is 75-85℃, and the reaction time is 5-7h; the organic solvent is selected from one or a combination of two of N-methylpyrrolidone, tetrahydrofuran, and N,N-dimethylformamide; anhydrous methanol or anhydrous ethanol is used as the washing agent, and the washing is performed 2-3 times; the drying is vacuum drying, the drying temperature is 50-70℃, and the drying time is 10-14h.

[0015] Further, in step S2, the mixed solvent is composed of anhydrous ethanol and deionized water in a volume ratio of (3-5):1; the silane coupling agent is γ-aminopropyltriethoxysilane, and its addition amount is 2-5% of the mass of the hydrophobic silica aerogel powder; the particle size of the hydrophobic silica aerogel powder is 10-100 nm.

[0016] Furthermore, in step S2, the hydrolysis-condensation reaction is carried out under acidic conditions. The pH of the reaction system is adjusted to 4.0-5.0 using glacial acetic acid, the reaction temperature is 50-70℃, and the reaction time is 2-4 hours. The drying is carried out under vacuum at a temperature of 60-80℃ for 8-12 hours. The centrifugation speed is 3000-5000 r / min, and the centrifugation time is 10-20 minutes.

[0017] Further, in step S3, the anhydrous organic solvent is selected from one or more of anhydrous ethanol, anhydrous toluene, or anhydrous tetrahydrofuran; the mass ratio of the ternary random copolymer to the aminated aerogel is (0.2-0.5):1; the stirring reaction temperature is 70-80℃, the reaction time is 3-5h, and ultrasonic dispersion is used during the reaction to enhance mass transfer; anhydrous ethanol is used as the washing agent, and the washing is performed 2-3 times; the drying is vacuum drying, the drying temperature is 60-80℃, and the drying time is 8-12h; the ultrasonic dispersion power is 200-400W, the frequency is 20-40kHz, and the ultrasonic time is 5-10min every 30min.

[0018] Further, in step S4, the intumescent flame retardant system is composed of ammonium polyphosphate, pentaerythritol, and aluminum hydroxide; the additives include dispersants, thickeners, film-forming aids, and defoamers; the dispersion is specifically as follows: first, pre-disperse at a speed of 800-1200 r / min for 20-30 min, then transfer to a sand mill, add zirconia beads and grind for 1-2 h; the mass ratio of ammonium polyphosphate, pentaerythritol, and aluminum hydroxide is (3-5):1:(2-4); the particle size of the zirconia beads is 0.8-1.2 mm, and the mass ratio of zirconia beads to the material is (1.5-2.5):1.

[0019] Further, the pretreatment in step S5 includes: sanding the aluminum alloy plate with sandpaper, ultrasonically cleaning it with anhydrous ethanol for 10-15 minutes, and drying it at 60-80℃ for 20-40 minutes; coating is done by air spraying, with a spraying pressure of 0.4-0.6MPa, a distance of 20-30cm between the spray gun and the aluminum plate, and spraying in 2-3 coats to control the dry film thickness to 180-220μm; drying and curing is a two-step curing process: first, surface drying at room temperature for 20-40 minutes, and then baking in a forced-air drying oven at 115-125℃ for 1.5-2.5 hours; the sandpaper mesh is 400-600; and the interval between each spray coat is 10-15 minutes.

[0020] Furthermore, the dispersant is selected from one or more of sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, sodium polyacrylate, sodium polycarboxylate SN-5040, sodium polycarboxylate BYK-190, sodium alkylnaphthalene sulfonate, and sodium lignosulfonate; the thickener is selected from one or more of hydroxyethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, thickener RM-8W, thickener TT-935, thickener ASE-60, and xanthan gum; the film-forming aid is selected from one or more of alcohol ester dodecyl, alcohol ester hexadecyl, diethylene glycol butyl ether, propylene glycol phenyl ether, and ethylene glycol butyl ether acetate. The coating comprises one or more of dipropylene glycol methyl ether, tripropylene glycol n-butyl ether, and hexanediol butyl ether acetate; the defoamer is selected from one or more of tributyl phosphate, polydimethylsiloxane emulsion, defoamer BYK-024, and defoamer NXZ; the amount of dispersant added is 0.5-1.2% of the total mass of the thermal insulation and flame retardant functional coating; the amount of thickener added is 0.3-0.8% of the total mass of the thermal insulation and flame retardant functional coating; the amount of film-forming aid added is 1.5-2.5% of the total mass of the thermal insulation and flame retardant functional coating; and the amount of defoamer added is 0.1-0.3% of the total mass of the thermal insulation and flame retardant functional coating.

[0021] According to another aspect of the present invention, a heat-insulating and flame-retardant functional coating for aluminum plates prepared by the above-described method is provided, which is prepared by means of raw materials comprising the following components:

[0022] The composition includes 38-42 parts of water-based silicone-acrylic emulsion, 16-18 parts of aerogel functional filler, 20-22 parts of intumescent flame retardant system, 2.5-3.5 parts of titanium dioxide, 3.3-5.8 parts of additives, and 17-19 parts of deionized water.

[0023] The aqueous silicone-acrylic emulsion has a solid content of 45-50% and a glass transition temperature of 15-25℃; the titanium dioxide is rutile titanium dioxide with a particle size of 200-300nm; the aluminum hydroxide has a particle size of 1-5μm; and the aluminum alloy plate is 3003 aluminum alloy plate or 5052 aluminum alloy plate with a thickness of 0.8-3.0mm.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention first introduces reactive epoxy groups, flame-retardant phosphorus elements, and rigid isoborneol units onto the same molecular chain via free radical polymerization. Then, a uniformly distributed active amino site is constructed on the surface of silica aerogel through a hydrolysis-condensation reaction of a silane coupling agent. Finally, a phosphorus-containing terpolymer is covalently anchored to the aerogel surface through an epoxy-amino ring-opening addition reaction, thus preparing an aerogel functional filler with an inorganic core-organic shell gradient structure. Relying on the similar solubility parameters between the organic shell and the aqueous silicone-acrylic emulsion matrix, as well as the multiple interfacial bonding effects composed of covalent bonds, hydrogen bonds, and molecular chain entanglements, molecular-level miscibility between the filler and the matrix is ​​achieved. This improves the weak interfacial mode of traditional inorganic fillers and organic matrices, which rely solely on van der Waals forces for bonding, alleviating phase separation and interfacial stress concentration problems caused by differences in surface energy between the two phases. Simultaneously, the steric hindrance effect of the organic shell suppresses the agglomeration tendency of aerogel particles. This interface control method helps to form a uniform and dense aggregated structure inside the coating, reducing the microscopic penetration channels caused by interface defects and filler agglomeration. It can effectively transfer and disperse external stress, improve the coating's protective ability and structural stability against aluminum substrates, and improve the problems of existing coatings being prone to cracking, peeling and substrate corrosion.

[0026] 2. This invention constructs a multi-mechanism synergistic insulation system combining aerogel thermal barrier, titanium dioxide thermal reflection, and thermal radiation, while simultaneously forming a multi-layered flame-retardant protective structure that complements the intrinsic flame retardancy of aerogel and the intumescent flame retardant system. Utilizing the dual inhibition of gas thermal convection and solid thermal conduction by the three-dimensional nanoporous network of aerogel, combined with the reflection of solar radiation and infrared radiation heat dissipation effect of titanium dioxide, it effectively suppresses the main heat transfer paths, alleviating the inherent contradiction between insulation and flame retardant performance in existing technologies, and reducing the problems of increased thermal conductivity and decreased insulation performance caused by the addition of large amounts of inorganic flame-retardant fillers. This synergistic mechanism can achieve good thermal insulation and flame retardant effects with relatively low filler addition, improving the overall thermal management performance and fire safety performance of the coating, and compensating for the shortcomings of limited insulation efficiency and insufficient flame retardant rating in existing products.

[0027] 3. This invention forms a rigid-flexible synergistic microstructure combining an inorganic rigid framework and an organic flexible matrix, while simultaneously achieving covalent bond immobilization of functional components. It relies on uniformly dispersed aerogel particles to transfer and disperse external forces, hindering crack propagation and absorbing fracture energy. The rigid monomer units in the graft copolymer enhance the overall rigidity of the molecular chain, improving the problems of mechanical property degradation, poor weather resistance, and easy migration and precipitation of functional components in traditional coatings. It also reduces the photochemical degradation of active silanol groups on the aerogel surface, significantly improving the coating's adhesion, flexibility, and scratch resistance, delaying the UV aging process, and helping to maintain the stability of thermal insulation and flame retardant properties during long-term service, thus improving the coating's service life and reliability. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] A method for preparing a heat-insulating and flame-retardant functional coating on the surface of an aluminum plate includes the following steps:

[0031] S1. 208g of diethyl vinylphosphonate, 100g of glycidyl methacrylate, and 313g of isobornyl methacrylate were dissolved in 2400mL of N-methylpyrrolidone, and 5.0g of azobisisobutyronitrile was added. The copolymerization reaction was carried out at 75℃ for 7h under nitrogen protection. After the reaction was completed, the reaction solution was slowly poured into 7200mL of anhydrous methanol to precipitate the product. The product was washed twice with 1000mL of anhydrous methanol and dried under vacuum at 50℃ for 14h to obtain a ternary random copolymer.

[0032] S2. 100g of hydrophobic silica aerogel powder with a particle size of 10nm was dispersed in a mixed solvent consisting of 750mL anhydrous ethanol and 250mL deionized water. 2.0g of γ-aminopropyltriethoxysilane was added, and 1.5mL of glacial acetic acid was added dropwise to adjust the pH of the system to 4.0. The reaction was carried out at 50℃ for 4h. After the reaction was completed, the mixture was centrifuged at 3000r / min for 20min, and the precipitate was washed twice with 600mL of anhydrous ethanol. The precipitate was then dried under vacuum at 60℃ for 12h to obtain an amino-modified aerogel.

[0033] S3. 100g of aminated aerogel was redispersed in 500mL of anhydrous ethanol, and 20g of ternary random copolymer was added. The mixture was stirred at 70℃ for 5h. During the reaction, ultrasonic dispersion at 200W and 20kHz was activated for 10min every 30min. After the reaction, the product was washed twice with 600mL of anhydrous ethanol and dried under vacuum at 60℃ for 12h to obtain the aerogel functional filler.

[0034] S4. Mix 160g of aerogel functional filler, 200g of intumescent flame retardant system (composed of 100g of ammonium polyphosphate, 33g of pentaerythritol and 67g of aluminum hydroxide), 25g of rutile titanium dioxide, 380g of waterborne silicone-acrylic emulsion with a solid content of 45% and a glass transition temperature of 15℃, 4.7g of sodium hexametaphosphate, 2.8g of hydroxyethyl cellulose, 14.0g of dodecyl alcohol ester and 0.9g of tributyl phosphate, and add 170g of deionized water. Pre-disperse at 800r / min for 30min, then transfer to a sand mill, add 1436g of zirconia beads with a particle size of 0.8mm and grind for 2h. After mixing, a heat-insulating and flame-retardant functional coating is obtained.

[0035] S5. Take a 3003 aluminum alloy plate with dimensions of 100mm × 100mm × 0.8mm, polish the surface with 400-grit sandpaper, ultrasonically clean it with anhydrous ethanol for 10 minutes, and then dry it at 60℃ for 40 minutes. Apply the coating to the surface of the aluminum plate using air spraying, with a spraying pressure of 0.4MPa, a distance of 20cm between the spray gun and the aluminum plate, and spray in two coats with a 10-minute interval between each coat, controlling the dry film thickness to 180μm. First, surface dry at room temperature for 40 minutes, and then dry in a forced-air environment at 115℃ for 2.5 hours to form a functional coating.

[0036] Example 2

[0037] A method for preparing a heat-insulating and flame-retardant functional coating on the surface of an aluminum plate includes the following steps:

[0038] S1. Dissolve 312g of diethyl vinylphosphonate, 100g of glycidyl methacrylate, and 469g of isobornyl methacrylate in 3500mL of tetrahydrofuran, add 8.8g of azobisisobutyronitrile, and copolymerize at 80℃ for 6h under nitrogen protection. After the reaction is complete, slowly pour the reaction solution into 14000mL of anhydrous ethanol to precipitate the product. Wash the product three times with 1500mL of anhydrous ethanol, and dry it under vacuum at 60℃ for 12h to obtain a ternary random copolymer.

[0039] S2. 100g of hydrophobic silica aerogel powder with a particle size of 50nm was dispersed in a mixed solvent consisting of 800mL anhydrous ethanol and 200mL deionized water. 3.5g of γ-aminopropyltriethoxysilane was added, and 1.8mL of glacial acetic acid was added dropwise to adjust the pH of the system to 4.5. The reaction was carried out at 60℃ for 3h. After the reaction was completed, the mixture was centrifuged at 4000r / min for 15min, and the precipitate was washed three times with 900mL of anhydrous ethanol. The precipitate was then vacuum dried at 70℃ for 10h to obtain an amino-modified aerogel.

[0040] S3. 100g of aminated aerogel was redispersed in 600mL of anhydrous toluene, and 35g of ternary random copolymer was added. The mixture was stirred at 75℃ for 4h. During the reaction, ultrasonic dispersion at 300W and 30kHz was activated for 7min every 30min. After the reaction, the product was washed three times with 900mL of anhydrous ethanol and dried under vacuum at 70℃ for 10h to obtain the aerogel functional filler.

[0041] S4. Mix 170g of aerogel functional filler, 210g of intumescent flame retardant system (composed of 105g ammonium polyphosphate, 26g pentaerythritol, and 79g aluminum hydroxide), 30g of rutile titanium dioxide, 400g of waterborne silicone-acrylic emulsion with a solid content of 47.5% and a glass transition temperature of 20℃, 8.1g of sodium polycarboxylate SN-5040, 5.2g of thickener RM-8W, 19.0g of propylene glycol phenyl ether, and 1.9g of polydimethylsiloxane emulsion, and add 180g of deionized water. Pre-disperse at 1000r / min for 25min, then transfer to a sand mill, add 1540g of zirconia beads with a particle size of 1.0mm, and grind for 1.5h. After mixing, a heat-insulating and flame-retardant functional coating is obtained.

[0042] S5. Take a 5052 aluminum alloy plate with dimensions of 100mm × 100mm × 1.9mm, polish the surface with 500-grit sandpaper, ultrasonically clean it with anhydrous ethanol for 13 minutes, and then dry it at 70℃ for 30 minutes. Apply the coating to the surface of the aluminum plate using an air spraying method, with a spraying pressure of 0.5MPa, a distance of 25cm between the spray gun and the aluminum plate, and spray in two coats with an interval of 13 minutes between each coat, controlling the dry film thickness to 200μm. First, surface dry at room temperature for 30 minutes, and then dry in a forced-air environment at 120℃ for 2.0 hours to form a functional coating.

[0043] Example 3

[0044] A method for preparing a heat-insulating and flame-retardant functional coating on the surface of an aluminum plate includes the following steps:

[0045] S1. 417g of diethyl vinylphosphonate, 100g of glycidyl methacrylate, and 626g of isobornyl methacrylate were dissolved in 4500mL of N,N-dimethylformamide, and 13.7g of azobisisobutyronitrile was added. The copolymerization reaction was carried out at 85℃ for 5h under nitrogen protection. After the reaction was completed, the reaction solution was slowly poured into 22500mL of anhydrous methanol to precipitate the product. The product was washed three times with 1800mL of anhydrous methanol and dried under vacuum at 70℃ for 10h to obtain a ternary random copolymer.

[0046] S2. 100g of hydrophobic silica aerogel powder with a particle size of 100nm was dispersed in a mixed solvent consisting of 833mL of anhydrous ethanol and 167mL of deionized water. 5.0g of γ-aminopropyltriethoxysilane was added, and 2.0mL of glacial acetic acid was added dropwise to adjust the pH of the system to 5.0. The reaction was carried out at 70℃ for 2h for hydrolysis and condensation. After the reaction was completed, the mixture was centrifuged at 5000r / min for 10min, and the precipitate was washed three times with 900mL of anhydrous ethanol. The precipitate was then vacuum dried at 80℃ for 8h to obtain an amino-modified aerogel.

[0047] S3. 100g of aminated aerogel was redispersed in 700mL of anhydrous tetrahydrofuran, and 50g of ternary random copolymer was added. The mixture was stirred at 80℃ for 3h. During the reaction, ultrasonic dispersion at 400W power and 40kHz frequency was turned on for 5min every 30min. After the reaction, the product was washed three times with 900mL of anhydrous ethanol and dried under vacuum at 80℃ for 8h to obtain the aerogel functional filler.

[0048] S4. Mix 180g of aerogel functional filler, 220g of intumescent flame retardant system (composed of 110g of ammonium polyphosphate, 22g of pentaerythritol and 88g of aluminum hydroxide), 35g of rutile titanium dioxide, 420g of waterborne silicone-acrylic emulsion with a solid content of 50% and a glass transition temperature of 25℃, 11.6g of sodium polycarboxylate BYK-190, 7.7g of xanthan gum, 24.1g of tripropylene glycol n-butyl ether and 2.9g of defoamer BYK-024, and add 190g of deionized water. Pre-disperse at 1200r / min for 20min, then transfer to a sand mill, add 1640g of zirconia beads with a particle size of 1.2mm and grind for 1h. After mixing, a heat-insulating and flame-retardant functional coating is obtained.

[0049] S5. Take a 3003 aluminum alloy plate with dimensions of 100mm × 100mm × 3.0mm, polish the surface with 600-grit sandpaper, ultrasonically clean it with anhydrous ethanol for 15 minutes, and then dry it at 80℃ for 20 minutes. Apply the coating to the surface of the aluminum plate using air spraying, with a spraying pressure of 0.6MPa, a distance of 30cm between the spray gun and the aluminum plate, and spray in 3 coats with an interval of 15 minutes between each coat, controlling the dry film thickness to 220μm. First, surface dry at room temperature for 20 minutes, and then dry in a forced-air dryer at 125℃ for 1.5 hours to form a functional coating.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 2 is that the covalent grafting reaction in step S3 is omitted. Instead, 100g of aminated aerogel and 35g of ternary random copolymer are physically mixed evenly and then added as filler to the coating system in step S4. The amounts of other raw materials and the preparation process are exactly the same as in Example 2.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 2 is that steps S1 and S3 are omitted, and 100g of unmodified hydrophobic silica aerogel powder is directly added as a filler to the coating system in step S4. The amount of other raw materials and the preparation process are exactly the same as in Example 2.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 2 is that 170g of hollow glass microspheres (particle size 50-80μm) were used to replace the aerogel functional filler. The remaining raw material amounts and preparation processes are exactly the same as in Example 2.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 2 is that the intumescent flame retardant system consists only of ammonium polyphosphate and pentaerythritol (mass ratio 4:1), with a total mass of 210g. No aluminum hydroxide is added, and the amounts of other raw materials and the preparation process are exactly the same as in Example 2.

[0058] Comparative Example 5

[0059] The difference between this comparative example and Example 2 is that in step S1, methyl methacrylate is used to replace diethyl vinylphosphonate to prepare the ternary random copolymer, while the amounts of other raw materials and the preparation process are exactly the same as in Example 2.

[0060] Coated aluminum plate samples were prepared according to the methods of Examples 1-3 and Comparative Examples 1-5 described above, and blank control group samples (5052 aluminum alloy plates that underwent only surface polishing, cleaning, and drying) were prepared. After all samples were prepared, they were placed in a standard environment at a temperature of 23±2℃ and a relative humidity of 50±5% for 24 hours for thermal and mechanical performance tests. The thermal performance tests included thermal insulation performance, flame retardant performance, vertical burning, and smoke density tests, while the mechanical performance tests included adhesion and adhesion strength.

[0061] (1) Thermal insulation performance test

[0062] The test was conducted according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method". Three parallel samples of 300mm × 300mm corresponding to the thickness of the aluminum plate were prepared for each formulation. The total thickness of each sample was measured at five locations (center and four corners) using a vernier caliper with an accuracy of 0.01mm. The average value was calculated and recorded. The thermal conductivity meter was turned on, with the hot plate temperature set to 35℃ and the cold plate temperature to 15℃. The instrument was preheated until the temperature fluctuation did not exceed ±0.1℃. The sample was placed flat between the hot and cold plates, ensuring close contact between the sample and the surfaces of the plates without any obvious gaps. The test program was started, and after the heat flux density stabilized (the deviation of three consecutive readings did not exceed 1%), the steady-state heat flux density value was recorded. The instrument automatically calculated and output the thermal conductivity of the sample in W / (m·K). The arithmetic mean of the test results of the three parallel samples in each group was taken as the final thermal conductivity.

[0063] (2) Flame retardant performance test

[0064] Referencing GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". Prepare three parallel samples of 150mm × 6.5mm thickness corresponding to the aluminum plate thickness for each formulation. Sand the edges of the samples to ensure they are smooth and burr-free. Turn on the oxygen index meter, preheat the instrument to room temperature, and adjust the total flow rate of oxygen and nitrogen to 10L / min. After the airflow stabilizes, begin the test. Clamp the sample vertically in the sample holder, ensuring the top of the sample is at least 100mm from the top of the combustion chamber. Adjust the oxygen concentration using a stepwise approximation method, igniting the sample at the top with an igniter for no more than 30s. If the combustion time exceeds 30s or the combustion length exceeds 50mm, decrease the oxygen concentration; conversely, increase the oxygen concentration. Repeat the above steps until the lowest oxygen concentration at which the sample can just sustain combustion is found. Record this as the limiting oxygen index (LOI) of the sample, expressed as a percentage. Take the arithmetic mean of the test results of three parallel samples in each group as the final limiting oxygen index.

[0065] (3) Vertical burning test

[0066] Referencing GB / T 8626-2007 "Test Methods for Flammability of Building Materials". Prepare three parallel samples of 125mm × 13mm thickness corresponding to the aluminum plate thickness for each formulation. Sand the edges of the samples to ensure they are smooth and burr-free. Turn on the vertical combustion tester, adjust the Bunsen burner flame height to 20mm, and preheat the flame until it is a uniform blue color. Clamp the sample vertically in the sample holder, with the lower end of the sample 10mm from the top of the Bunsen burner. Apply the flame to the sample for 15s, then quickly remove the Bunsen burner, recording the flaming and flameless combustion times. Observe and record the burning length of the sample, and whether there is any dripping. Evaluate the flammability rating of the samples according to GB / T 8626-2007. Take the arithmetic mean of the test results of the three parallel samples in each group as the final burning time and burning length.

[0067] (4) Smoke density test

[0068] Referring to GB / T 8323.2-2008 "Plastic Smoke Generation Part 2: Determination of Smoke Density by Single Chamber Method". For each formulation, prepare three parallel samples of 75mm × 75mm corresponding to the thickness of the aluminum plate, ensuring the sample surfaces are flat and defect-free. Turn on the smoke density meter, preheat the instrument to room temperature, and check the airtightness of the test chamber to ensure no leakage. Place the sample on the sample holder with the coated side facing the radiation source. Close the test chamber door, turn on the radiation source and igniter, and begin the test. The instrument automatically records the change in optical density during the test, which lasts for 20 minutes. After the test, record the maximum smoke density (DSmax) of each sample. The arithmetic mean of the test results of the three parallel samples in each group is taken as the final maximum smoke density.

[0069] (5) Adhesion test

[0070] Refer to GB / T 9286-1998 "Cross-cut test for paint and varnish films". Prepare three parallel samples of 150mm × 100mm thickness corresponding to the aluminum plate thickness for each formulation, ensuring the sample surface is clean and dry. Using a 6-blade cross-cutting tool, cut six parallel cutting lines with a spacing of 1mm on the sample coating surface, the cutting depth should penetrate the coating to the substrate surface. Then cut six more lines perpendicular to the above cutting lines to form 25 1mm × 1mm squares. Gently brush away any loose debris in the square area with a soft brush, and smoothly apply 3M tape to the square area, pressing the tape firmly with your fingers to ensure complete contact between the tape and the coating. Holding one end of the tape, quickly peel it off at a 60° angle to the coating surface. Visually observe the coating peeling in the square area, and evaluate the adhesion grade according to GB / T 9286-1998 standard (grade 0 is the best, grade 5 is the worst). Take the mode of the test results of the three parallel samples in each group as the final adhesion grade.

[0071] (6) Adhesion

[0072] Refer to GB / T 1731-1993, "Determination of Coating Film Flexibility". Prepare three parallel samples (150mm × 100mm) corresponding to the thickness of an aluminum plate for each formulation, ensuring the sample surfaces are clean and dry. With the coated side facing up, fix one end of the sample to the shaft of the shaft flexibility tester, with the shaft diameter decreasing sequentially from 10mm. Bend the sample 180° around the shaft at a uniform speed for 2-3 seconds. Observe the coating surface using a 4x magnifying glass for any cracks or peeling. Record the minimum shaft diameter (in mm) at which no cracks or peeling occur. Take the minimum value from the three parallel samples in each group as the final flexibility test result.

[0073] The experimental results are shown in Table 1-2:

[0074] Table 1. Thermal performance test results of functional coatings on the surface of various thermal insulation and flame retardant aluminum plates

[0075]

[0076] Table 2. Test results of mechanical properties of functional coatings on the surface of various thermal insulation and flame retardant aluminum panels

[0077]

[0078] As shown in Table 1, the thermal conductivity of Examples 1-3 is stable at 0.031-0.035 W / (m·K), the limiting oxygen index exceeds 31%, the vertical combustion rating reaches B1, the flaming combustion time is only 2-4 s with no flaming combustion, and the maximum smoke density is controlled between 74-79. This indicates that the thermal insulation and flame retardant aluminum plate surface functional coating prepared by this invention possesses both excellent thermal insulation performance and efficient low-smoke flame retardant performance. This invention constructs an aerogel functional filler with an inorganic core-organic shell gradient structure through a covalent grafting process. This filler achieves uniform dispersion at the single-particle level in an aqueous silicone-acrylic emulsion matrix, completely preserving the three-dimensional nanoporous network structure of the aerogel. This confines air molecules within pores smaller than their mean free path, effectively suppressing gas thermal convection. Simultaneously, the multiple scattering of phonons by the nanoscale silica framework significantly reduces the solid thermal conductivity, thus achieving excellent thermal insulation effects. In terms of flame retardancy, this invention constructs a multi-level synergistic protection mechanism of intrinsic flame retardancy of aerogel and intumescent flame retardancy system. The phosphorus-containing terpolymer grafted on the surface of aerogel can catalyze the early dehydration and carbonization of resin and capture combustion-active free radicals. The intumescent flame retardant system plays its role in different temperature ranges to form a thick and dense intumescent char layer. Silica aerogel, as an inorganic skeleton, further enhances the mechanical strength and thermal stability of the char layer. The synergistic effect of the three achieves efficient flame retardancy and reduces smoke generation.

[0079] The thermal conductivity of Comparative Example 1 and Comparative Example 2 increased to 0.041 W / (m·K) and 0.046 W / (m·K), respectively, while the limiting oxygen index decreased to 28.6% and 27.4%, respectively. The vertical combustion rating dropped to B2, and the smoke density also increased significantly. This is because Comparative Example 1 omitted the covalent grafting reaction, and the aminated aerogel and terpolymer were only physically mixed. The filler was prone to local agglomeration, which destroyed the continuous porous insulation structure. At the same time, the phosphorus-containing groups were unevenly distributed, making it impossible to form a continuous catalytic char-forming interface. Comparative Example 2 directly used unmodified hydrophobic silica aerogel, which has extremely poor compatibility with the organic resin matrix. The agglomeration phenomenon was even more serious, and a large number of pores were compressed or filled. In addition, it lacked the intrinsic flame-retardant effect of the phosphorus-containing copolymer, resulting in a significant decrease in both insulation and flame-retardant performance. Comparative Example 3, which replaced the aerogel functional filler with hollow glass microspheres, exhibited a thermal conductivity as high as 0.056 W / (m·K), a limiting oxygen index of only 26.2%, and a smoke density of 10³, making it the worst performing sample in terms of both thermal insulation and flame retardancy. This is because the micron-sized pores of the hollow glass microspheres cannot effectively suppress gas thermal convection, and the solid-state thermal conductivity of the glass microspheres is far higher than that of the aerogel nanoframework. Furthermore, the glass microspheres themselves lack flame retardant activity, and their high porosity structure provides ample oxygen channels for combustion. Comparative Examples 4 and 5 showed thermal conductivity similar to the examples, but their limiting oxygen indices decreased to 29.5% and 25.4%, respectively. This indicates that the thermal insulation performance is mainly determined by the structure and dispersion state of the aerogel filler, while the flame retardant performance is highly dependent on the intrinsic flame retardant effect of the phosphorus-containing copolymer and the synergistic effect of the intumescent flame retardant system.

[0080] As shown in Table 2, the adhesion grade of Examples 1-3 is 0-1, and the flexibility is 1-2 mm, indicating that the coating prepared by this invention has a strong bond with the aluminum substrate and also possesses good flexibility and resistance to deformation. This invention covalently grafts a phosphorus-containing terpolymer onto the aerogel surface through an epoxy-amino ring-opening addition reaction, forming a multi-layered interfacial bonding structure between the filler and the aqueous silicone-acrylic emulsion matrix, composed of covalent bonds, hydrogen bonds, and molecular chain entanglements, significantly improving the interfacial bonding energy. This strong interfacial bonding effectively transfers and disperses external stress, preventing coating cracking and peeling caused by stress concentration. Simultaneously, the uniformly dispersed aerogel particles act as nano-toughening agents, deflecting, bifurcating, and bridging when cracks propagate, absorbing a large amount of fracture energy and significantly improving the coating's flexibility. Furthermore, the isobornyl methacrylate unit in the terpolymer has a bicyclic rigid structure, enhancing the overall rigidity of the molecular chain and further improving the mechanical strength of the coating.

[0081] The adhesion grades of Comparative Examples 1 and 2 decreased to grades 2 and 3, respectively, and their flexibility deteriorated to 3 mm and 5 mm, respectively. This is because neither formed an effective covalent bond interface; only weak van der Waals forces existed between the filler and the substrate, resulting in weak interfacial bonding and a tendency for interfacial debonding. Furthermore, the numerous defects caused by filler agglomeration led to severe stress concentration, making the coating highly susceptible to cracking and peeling under external forces. Comparative Example 3 showed an adhesion grade of 2 and a flexibility of 4 mm, with significantly deteriorated mechanical properties. This is because the hollow glass microspheres had smooth surfaces and lacked reactive groups, resulting in weak interfacial bonding with the substrate. Additionally, the glass microspheres themselves were brittle and unable to provide nano-toughening. The mechanical properties of Comparative Examples 4 and 5 were similar to those of the examples, indicating that the mechanical properties of the coating are mainly determined by the interfacial modification effect of the aerogel, with adjustments to the flame-retardant components having a relatively small impact on the mechanical properties.

[0082] In summary, this invention utilizes a multi-level interface control process involving ternary random copolymerization, amination modification of the aerogel surface, and epoxy-amino covalent grafting to construct a core-shell aerogel functional filler. This effectively solves the core problems of poor compatibility between inorganic fillers and organic matrices, and the mutual constraint between thermal insulation and flame retardant properties in traditional thermal insulation and flame retardant coatings. Experimental results show that the coating prepared by this invention is significantly superior to the comparative examples in terms of thermal insulation, flame retardancy, smoke suppression, and mechanical properties.

[0083] In the description of this specification, the reference to terms such as "example," "various examples," etc., means that a specific feature, structure, material, or characteristic described in connection with that example or preparation is included in at least one example or preparation of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparations.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a functional coating on the surface of a thermally insulating and flame-retardant aluminum plate, characterized in that, Includes the following steps: S1. Diethyl vinylphosphonate, glycidyl methacrylate and isobornyl methacrylate are dissolved in an organic solvent and copolymerized under the action of an initiator. The product is precipitated, washed and dried to obtain a ternary random copolymer. S2. Disperse hydrophobic silica aerogel powder in a mixed solvent, add silane coupling agent, carry out hydrolysis and condensation reaction, and obtain aminated aerogel by centrifugation, washing and drying. S3. The aminated aerogel is redispersed in an anhydrous organic solvent, a ternary random copolymer is added, the mixture is stirred and reacted, and after the reaction is completed, it is washed, centrifuged and dried to obtain the aerogel functional filler. S4. Mix aerogel functional filler with an intumescent flame retardant system, titanium dioxide, water-based silicone-acrylic emulsion and additives, add deionized water, and then disperse, mill and adjust the paint to obtain a heat-insulating and flame-retardant functional coating. S5. Apply the heat-insulating and flame-retardant functional coating to the surface of the pretreated aluminum alloy plate, and then dry and cure it to form a functional coating.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of diethyl vinylphosphonate, glycidyl methacrylate, and isobornyl methacrylate is (2.08-4.17):1:(3.13-6.26); the initiator is selected from azobisisobutyronitrile, and its addition amount is 0.8-1.2% of the total mass of diethyl vinylphosphonate, glycidyl methacrylate, and isobornyl methacrylate.

3. The preparation method according to claim 1, characterized in that, The copolymerization reaction in step S1 is carried out under inert gas protection at a temperature of 75-85℃ for 5-7 hours. The organic solvent is selected from one or a combination of two of N-methylpyrrolidone, tetrahydrofuran, and N,N-dimethylformamide.

4. The preparation method according to claim 1, characterized in that, In step S2, the mixed solvent is composed of anhydrous ethanol and deionized water in a volume ratio of (3-5):1; the silane coupling agent is γ-aminopropyltriethoxysilane, and its addition amount is 2-5% of the mass of hydrophobic silica aerogel powder.

5. The preparation method according to claim 1, characterized in that, In step S2, the hydrolysis-condensation reaction is carried out under acidic conditions. The pH of the reaction system is adjusted to 4.0-5.0 by glacial acetic acid, the reaction temperature is 50-70℃, and the reaction time is 2-4h. The drying is carried out under vacuum at a temperature of 60-80℃ for 8-12h.

6. The preparation method according to claim 1, characterized in that, In step S3, the anhydrous organic solvent is selected from one or more of anhydrous ethanol, anhydrous toluene, or anhydrous tetrahydrofuran; the mass ratio of the ternary random copolymer to the aminated aerogel is (0.2-0.5):1; the stirring reaction temperature is 70-80℃, the reaction time is 3-5h, and ultrasonic dispersion is used during the reaction to enhance mass transfer; anhydrous ethanol is used as the washing agent, and the washing is performed 2-3 times; the drying is vacuum drying, the drying temperature is 60-80℃, and the drying time is 8-12h.

7. The preparation method according to claim 1, characterized in that, In step S4, the intumescent flame retardant system is composed of ammonium polyphosphate, pentaerythritol and aluminum hydroxide; the additives include dispersant, thickener, film-forming aid and defoamer; the dispersion is as follows: first, pre-disperse at a speed of 800-1200 r / min for 20-30 min, then transfer to a sand mill and add zirconia beads to grind for 1-2 h.

8. The preparation method according to claim 1, characterized in that, The pretreatment in step S5 includes: sanding the aluminum alloy plate with sandpaper, ultrasonically cleaning it with anhydrous ethanol for 10-15 minutes, and drying it at 60-80℃ for 20-40 minutes; coating is done by air spraying, with a spraying pressure of 0.4-0.6MPa, a distance of 20-30cm between the spray gun and the aluminum plate, and spraying in 2-3 coats to control the dry film thickness to 180-220μm; drying and curing is a two-step curing process: first, surface drying at room temperature for 20-40 minutes, and then baking it in a forced-air drying oven at 115-125℃ for 1.5-2.5 hours.

9. The preparation method according to claim 7, characterized in that, The dispersant is selected from one or more of sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, sodium polyacrylate, sodium polycarboxylate SN-5040, sodium polycarboxylate BYK-190, sodium alkylnaphthalene sulfonate, and sodium lignosulfonate; the thickener is selected from one or more of hydroxyethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, thickener RM-8W, thickener TT-935, thickener ASE-60, and xanthan gum; the film-forming aid is selected from one or more of alcohol ester dodecyl, alcohol ester hexadecyl, diethylene glycol butyl ether, propylene glycol phenyl ether, ethylene glycol butyl ether acetate, dipropylene glycol methyl ether, tripropylene glycol n-butyl ether, and hexanediol butyl ether acetate; the defoamer is selected from one or more of tributyl phosphate, polydimethylsiloxane emulsion, defoamer BYK-024, and defoamer NXZ.

10. A functional coating for the surface of a heat-insulating and flame-retardant aluminum plate prepared by the preparation method according to any one of claims 1-9, characterized in that, It is prepared from raw materials comprising the following components, by weight: The composition includes 38-42 parts of water-based silicone-acrylic emulsion, 16-18 parts of aerogel functional filler, 20-22 parts of intumescent flame retardant system, 2.5-3.5 parts of titanium dioxide, 3.3-5.8 parts of additives, and 17-19 parts of deionized water.

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